Interactions of the DNA mismatch repair proteins MLH1 and MSH2 with c-MYC and MAX

Area of Science:

• Molecular Biology
• Cancer Research
• Genetics

Background:

• DNA mismatch repair (MMR) proteins MSH2 and MLH1 are crucial for DNA replication fidelity and apoptosis induction by anticancer agents.
• The precise function of MLH1 in MMR and apoptosis signaling remains incompletely understood.
• Identifying novel MLH1 interaction partners can elucidate its role in DNA repair and cell death pathways.

Purpose of the Study:

• To identify novel interaction partners of human MLH1 involved in MMR or apoptosis signaling.
• To investigate the functional consequences of MLH1 interactions with identified partners, particularly c-MYC.

Main Methods:

• Yeast two-hybrid screening of human breast and ovarian cDNA libraries using human MLH1.
• In vitro experiments including GST-fusion pull-down assays.
• In vivo experiments utilizing co-immunoprecipitation from human tumor cell extracts and inducible c-MYC-ER fusion gene expression in Rat1 cells.

Main Results:

• MLH1 was found to interact with the carboxy terminus of the human c-MYC proto-oncogene, in addition to known partners like PMS1, MLH3, and MBD4.
• Interaction between MLH1 and c-MYC was confirmed both in vitro and in vivo.
• The c-MYC partner protein MAX was shown to interact with MSH2.
• Elevated c-MYC expression led to a modest but consistent increase in the HGPRT mutation rate and frameshift mutants in Rat1 cells, suggesting partial inhibition of MMR.

Conclusions:

• MLH1 directly interacts with the c-MYC protein, suggesting a potential role for c-MYC in regulating DNA mismatch repair.
• The interaction between c-MYC and MLH1, and MAX and MSH2, highlights a novel molecular link between proto-oncogene regulation and DNA repair machinery.
• Deregulated c-MYC expression may impair MMR activity, potentially contributing to genomic instability and cancer development.